As electronic systems are provided with higher performances, more sophisticated functions and smaller sizes, semiconductor devices and wiring boards to be used for the electronic systems are required to work at higher speed or to be mounted in higher density. Thus, semiconductor devices such as a chip scale package (CSP), a multi-chip module and a system in package (SiP) have been developed.
As one of such package forms, a form having a plurality of surface mount leads such as an SOP (Small Outline Package) and a QFP (Quad Flat Package) is widely used. The leads each are of a so-called gull wing type or a J-lead type, and are connected to mount pads formed on a surface of a wiring board.
As high density mounting progresses, lots of leads and mount pads have come to be arranged at a narrow pitch down to, e.g., 0.3 mm pitch. Such narrow pitch arrangements are likely to cause a problem in that a solder bridge or something causes a short circuit between adjacent mount pads. In order to deal with such a problem, a method is proposed for making every other surface mount lead into different shapes so as to shift positions of the mount pads and to broaden separations between the adjacent mount pads. Further, a method is proposed for mixing surface mount leads and insert leads to be inserted into through holes of a wiring board.
The followings are reference documents.    [Document 1] Japanese Laid-open Patent Publication No. 04-28259.    [Document 2] Japanese Laid-open Patent Publication No. 05-291468.    [Document 3] Japanese Laid-open Patent Publication No 07-312403.    [Document 4] Japanese Laid-open Patent Publication No. 2007-13040.